1. Field of the Invention
The present invention relates to control devices for adjusting control values such as the output torque and rotation speed of an electric rotary machine, and in particular, the control device controls an electric power conversion circuit equipped with switching elements so as to selectively open and close electric connection lines between a voltage supply unit capable of supplying a different voltage and terminals of the electric rotary machine in order to adjust the control values of the electric rotary machine.
2. Description of the Related Art
For example, there is a control device for performing a triangle-wave comparison PWM (pulse width modulation). The control device calculates an instruction voltage of each phase of a three phase electric rotary machine, and compares the calculated instruction voltage of each phase with a triangle-wave carrier, and selectively operating switching elements which form an inverter as an electric power conversion circuit of the electric rotary machine on the basis of the comparison result. Such a control device is available in the commercial market.
Recently, there is a conventional control device, for example, disclosed in a Japanese patent laid open publication No. JP 2008-228419, which performs a prediction model control capable of predicting a current which flows in each phase of a three-phase electric rotary machine under various operation states of an inverter, The conventional control device then adjusts the inverter so as to operate under the operation state with a minimum difference value between the predicted current value and an instruction current value. Because such a prediction model control adjusts the operation state of the inverter to the optimum operation state having an optimum current value which has been predicted on the basis of the output voltage of the inverter, this makes it possible to increase the accuracy of the follow-up control signal which follows the instruction current when the inverter enters its transition state when compared with the accuracy obtained by the triangle-wave PWM control previously described.
It can be understood for the above prediction model control to be applied to high accuracy applications such as a device for controlling a motor generator (alternator) as an on-vehicle main machine which needs to perform the follow-up control with high accuracy.
There is another conventional technique to perform the above prediction model control. For example, Japanese patent laid open publication No. JP 2006-174697 discloses such a conventional technique to perform the prediction model control.
However, the more an electrical angular velocity of an electric rotary machine increases and the period of time of updating the operation state of the electric rotary machine becomes long, the more the control accuracy decreases.